There seem to be some conflicting results from test flights. Perhaps it is just a matter of where the different flights flew. Some test by civilian airliners showed no damage to engines but military fighter jet flights showed some damage to the engines. At least the cloud seems a bit less extensive now and some flights have already resumed today. I imagine if they fly somewhat lower the situation might be better. THis is from abc(Australia)
Fighter jet engines suffer volcano damage
NATO fighter jets have returned from flying through some of Iceland's drifting ash plume, and have reportedly suffered engine damage.
On Sunday, test flights in England, France Germany and the Netherlands, returned seemingly safely, with pilots reporting no problems. Their engines are still being examined.
But today, several NATO F-16 fighter jets have suffered damage, with glass fragments being found in their engines.
It comes not long after several airlines appealed for the regulator to review the blanket airspace restrictions.
The UK has called in three navy ships to help stranded commuters from Spain and other channel ports.